Study On The Effect Of Y Element On Relaxation And Compression Behavior Of Cu-Zr-Al-Y Metallic Glasses

Metallic glasses have the potential to be the kinds of important engineering materials because of their obvious advantages in many properties.However,the lack of ductility of metallic glasses at room temperature has severely hindered their practical application.The relaxation is an intrinsic and universal feature of supercooled liquids and glasses,and it is of significant importance for understanding the key issues in physics and material sciences,such as the glass transition phenomenon,diffusion,physical aging,mechanisms of plastic deformations,as well as stability and crystallization of glassy materials,etc.In metallic glass systems,rare earth-based metallic glasses generally have pronouncedβrelaxation,while metallic glasses with pronouncedβrelaxation behaviors are more likely to have ductility.It is important to explore the relationship between composition and ductile deformation or the relaxation.Therefore,the effect of Y element onβrelaxation and compression behavior of Cu-Zr-Al-Y metallic glasses is proposed in this paper.In this paper,the Cu₄₆Zr_47-xAl₇Y_x（x=1,3,5）as-cast alloys with complete amorphous structure were prepared.The glass transition temperature,the crystallization onset temperature and the supercooled liquid region of metallic glasses were examined by differential scanning calorimetry.The results show that as the Y element increases,the supercooled liquid region are improved simultaneously,thus the conclusion that Cu46Zr42Al7Y5 metallic glass has stronger amorphous formation ability and thermodynamic stability in the Cu-based metallic glass system was obtained.Using by dynamic mechanical analyzer,theβrelaxation behaviors of Cu₄₆Zr_47-xAl₇Y_x（x=1,3,5）metallic glasses was characterized by two experimental conditions of fixed frequency and frequency conversion.The results show that under the condition of fixed frequency,theβrelaxation becomes more pronounced with the increase of Y element content;under the condition of frequency conversion rate,the peak temperature ofβrelaxation of three metallic glasses have the tendency to move obviously towards higher temperature direction with the increase of frequency.Meanwhile,it was also found that the behavior of theβrelaxation is related to the enthalpy of mixing and the mean chemical affinity.The Cu₄₆Zr₄₂Al₇Y₅ metallic glass with the minimum negative values of the mean chemical affinity shows the most pronouncedβrelaxation.In addition,a series of compression tests were performed on the Cu₄₆Zr₄₄Al₇Y₃ metallic glass at different strain rates and a wide temperature range.The results show that the plastic strain variables increased correspondingly with the increase of temperature at the same strain rate,while at the same temperature,the higher strain rate,the lower plastic strain variables.The fracture surfaces of metallic glasses after compression experiments were examined via scanning electron microscopy.The fracture surface has a typical choroid pattern and its direction is consistent with the expansion direction of the shear zone.Meanwhile,using by the Arrhenius equation fitting,the activation energy ofβrelaxation and the apparent activation energy of brittle-to-ductile transition are 154±5 kJ/mol and 165±5 kJ/mol,respectively.The equivalent activation energy values indicate that both the brittle-to-ductile transition andβrelaxation are essentially from the same origin.